In a solid polymer electrolyte fuel battery, membrane-electrode assemblies (MEAs) and separators are alternately arranged. The MEA is composed of an ion-exchange electrolyte membrane, an anode (fuel electrode) arranged on one surface of the electrolyte membrane, and a cathode (oxygen electrode) arranged on the other surface of the electrolyte membrane. The separators form fluid passages for respectively supplying fuel gas (hydrogen) and oxidant gas (oxygen, normally air) to the anode and the cathode. The fuel battery has a stack structure in which unit cells (electric cells) each composed of an MEA and a separator are stacked and integrated. Since the solid polymer electrolyte fuel battery has advantages of easy miniaturization, operation at low temperatures and others, it is attracting attention particularly as a power supply for a moving body such as a vehicle.
Miniaturization and lower cost for fuel batteries of this type have been sought for practical use. In this respect, a cooling system and a humidification system can be simplified if a fuel battery is operable under high temperature and no humidity.
Patent Document 1 discloses a fuel battery operable under high temperature and no humidity which is configured to, when the moisture content is insufficient near the oxidant gas flow passage inlet, which is most likely to become dry, i.e. in the upstream section of the oxidant gas flow passage, increase the moisture content near the inlet of the oxidant gas flow passage by increasing a fuel gas flow rate or decreasing a fuel gas pressure.
Patent Document 2 discloses a fuel battery having a transverse section as shown in FIG. 12. Each unit cell 100 of the fuel battery includes a membrane-electrode assembly (MEA) 108 and a pair of separators 110, 112. The membrane-electrode assembly 108 is so structured that a polymer electrolyte membrane 102 is sandwiched between a cathode (oxygen electrode) 104 and an anode (fuel electrode) 106. The separators 110, 112 of each unit cell 100 are arranged to sandwich the membrane-electrode assembly 108. An oxidant gas flow passage 114 is formed between the separator 110 and the cathode 104. A fuel gas flow passage 116 is formed between the separator 112 and the anode 106. The cathode 104 is formed by laminating a cathode catalyst layer 104a and a gas diffusion layer 104b. The anode 106 is formed by laminating an anode catalyst layer 106a and a gas diffusion layer 106b. Each separator 110, 112 includes a plurality of grooves. The grooves of the separator 110 of each unit cell 100 are located to face the grooves of the separator 112 of a unit cell 110 adjacent to the same unit cell 100, and a cooling medium flow passage 120 is formed by these grooves facing each other. Since the cooling medium flow passages 120 are provided near the membrane-electrode assemblies 108, the fuel battery is efficiently cooled with a low thermal resistance by a cooling medium (e.g. cooling water) flowing in the cooling medium flow passages 120.
Patent Document 3 discloses a fuel battery having a transverse section as shown in FIG. 13. In FIG. 13, components corresponding to those of the fuel battery of FIG. 12 are denoted by the same reference signs as in FIG. 12. In the fuel battery of FIG. 13, gas diffusion porous bodies 130, 140 are respectively provided in a fuel gas flow passage 116 and an oxidant gas flow passage 114 to uniformly diffuse gases in the entireties of the respective fuel gas flow passage 116 and oxidant gas flow passage 114, thereby enhancing the performance of the fuel battery.
Further, in a fuel battery disclosed in Patent Document 4, a water-conducting layer is provided in a gas diffusion porous body to improve the drainability of water produced in the fuel battery.